Magnetron



Feb. 1965 J. DREXLER ETAL MAGNETRON Filed April 26. 1961' INVENTORS JEROME DREXLER RQBER NGLE FRED A. FEQLNER 3,169,211 MAGNETRON Jerome Drexler, New Providence, Robert Angle, Scotch Plains, and Fred A. Feulner, Green Village, N.l'., assignors to S-F-D Laboratories Inc, Union, N .J a corporation of New Jersey Filed Apr. 26, 1961, Ser. No. 165,715 17 (Ilaims. (Cl. 31539.77)

The present invention relates in general to electron discharge devices of the magnetron type and more specifically to a coaxial cavity type magnetron useful for generating high power microwave energy such as required in high power radars, linear accelerators, microwave heating devices and the like.

Heretofore a coaxial cavity type magnetron has been built operating at approximately 17 kilomegacycles and generating a peak R.F. power of approximately 100 kilowatts with an average RF. power of 100 watts. When an attempt is made to push this prior art design to RF. power levels of one megawatt peak, and 1000 watts average R.F. power at frequencies of approximately kilomegacycles, several severe problems are encountered which prevent attaining these latter specifications.

Some of the problems associated with pushing the power output of the prior art coaxial magnetron to the higher power levels are as follows: The slot mode suppressor design utilized in the prior art coaxial cavity magnetron was insufficiently cooled thereby prohibiting its use at higher power levels. The prior art magnetron vanes forming the anode cavities had a height at their base near the coupling slots which was substantially the same as the height of the vanes at their tips opposite the cathode. Accordingly, the anode resonators had a lower peak power handling capability for a given circuit Q. Also, insufficient coupling was obtained between the unwanted TE mode in the coaxial cavity and the coaxial cavitys TE mode suppressor whereby this undesired mode interfered with operation in the desired mode thereby causing the magnetron to misfire. In addition, insufficient cooling of the magnetron body was obtained for average RF. power levels in the order of 900 watts.

One further problem associated with the prior art magnetron was that the cathode pole piece construction considerably complicated cathode construction and cathode replacement.

The coaxial magnetron tube of the present invention solves the aforementioned difiiculties associated with the prior art tube and provides a 10K mc. magnetron havingpeak RF. power output in the order of one megawatt with average R.F. power output of approximately 1000 watts and yielding over-all efiiciencies of approximately 55%. This tube represents an enhancement of approximately one order of magnitude over that obtained by the prior art coaxial magnetron tube.

The principal object of the present invention is to provide an improved high power coaxial magnetron tube yielding substantially enhanced peak and average RF. power with increased efiiciency.

One feature of the present invention is the provision of a split internal cathode magnetic circuit construction which facilitates initial construction and subsequent replacement of the cathode portion of the magnetron.

Another feature of the present invention is the provision of an axe-shaped anode vane member, the base of the vane being shorter than the free end of the vane, whereby for a given vane tip area a higher Q for the anode resonators is obtained resulting in more eflicient operation for the tube.

Another feature of the present invention is the provision of lossy slot mode suppressor element formed and 3,l69,2ll Patented Feb. 9, 1965 arranged within a heat sinking retaining groove and dimensioned such that as the mode suppressor element begins to absorb power, the thermally produced expensive forces generated in the lossy member cause it to expand radially outwardly against the side walls of the retaining groove to produce cooling thereof by thermal conduction from the lossy member to the walls of the groove forming a heat sink. In this manner, overheating of the slot mode suppressor element is prevented in use thereby permitting the tube to operate at much higher average power levels without interference from the undesired slot mode.

Another feature of the present invention is the provision of an annular groove in a fixed end wall of the outer coaxial cavity. The groove is further arranged at the intersecting corner of the outer cavity and the slotted anode wall on the opposite side of the anode wall from the slot mode absorber and is made axially coextensive with both the end portions of the slots and the slot mode absorber whereby coupling of the slot mode absorber to the undesired slot mode and to the undesired TE mode is obtained without coupling to the desired TE mode of the outer coaxial cavity resulting in more stable operation of the coaxial magnetron.

Another feature of the present invention is the provision of closely spaced fin portions inwardly extending of an annular liquid coolant chamber provided in the main body portion of the coaxial magnetron tube for enhancing thermal conduction of energy from the tube to the liquid coolant to prevent overheating of the magnetron in use.

Other features and advantages of the present invention will become apparent upon a perusal of the specification taken in connection with the accompanying drawings wherein:

FIG. 1 is an outside perspective view of the coaxial magnetron tube of the present invention,

FIG. 2 is an enlarged partial cross-sectional view of the structure of FIG. 1 taken along line 2--2 in the direction of the arrows,

FIG. 3 is a fragmentary enlarged cross-sectional view of a portion of the structure of FIG. 2 taken along line 3-3 in the direction of the arrows,

FIG. 4 is an enlarged fragmentary cross-sectional view of a portion of the structure of FIG. 2 delineated by line 44,

FIG. 5 is an enlarged cross sectional view of a portion of the structure of FIG. 1 taken along line 5-5 in the direction of the arrows.

Referring now to FIGS. 1 and 2 character 1 represents the main supporting body of the coaxial magnetron, as of copper, to which other parts are brazed or otherwise suitably fastenedvto form a structure capable of being evacuated. On opposite sides of the body 1, there are brazed to the body 1 tubular envelope sections forming anode envelope 2 and cathode envelope 3, respectively.

The cathode envelope 3 includes a plurality of tubular segments 4, 7, 8, 12 and 13 joined together at their ends in a vacuum tight manner. A take-apart joint is formed by mating flange members 5 and 6 and divides the cathode envelope into one fixed and one detachable subassembly. The detachable subassembly includes flange 6 and is readily attached or detached as a unit thereby facilitating initialfabrication and subsequent replacement of the cathode. Tubular cathode segment 7 is made of a dielectric material as of, for example, glass and forms a high voltage insulator for holding off the high voltage applied between anode and cathode of the magnetron tube, in use. Insulator 7 is provided with an outwardly directed bulge to increase the current leakage path thereby increasing the voltage rating of the insulator 7.

A re-entrant portion of the cathode envelope 3 is formed by metallic tubular segment 12. Segment 12 is provided with an inwardly converging centrally apertured end portion, the inner margin of the central opening in member 12 encompassing in abutting relationship and being sealed, in a vacuum tight manner, at 11 to a sleeve portion of a cylindrical cathode emitter 9.

The cathode sleeve 19 has a substantial portion thereof extending outwardly of the vacuum envelope, within the re-entrant portion of the vacuum envelope. This additional external portion of the cathode sleeve 10 readily permits access thereto for lending additional physical support to the cathode assembly. It also readily permits application of operating potentials and cooling techniques as required. The additional physical support for the cathode sleeve 10 is obtained from the inner wall of the re-entrant envelope segment 12 via open-ended cylindrical baflle and transverse header 14. Header 14 is carried within baffie 15 and is fixedly secured to the cathode sleeve 10 substantially at the outer end thereof. Baflle 15 is supported within the tubular re-entrant segment 12 of the cathode envelope 3 via the intermediary of a plurality of dielectric spacing members 16 placed at spaced intervals about the periphery of the bafile 15 and being carried therefrom and bearing in slidable engagement with the surface of cathode envelope segment 12. A cathode heating element, not shown, is carried within cathode sleeve member 10 in a conventional manner.

Independent cathode heater potentials and currents are supplied to the heating element via terminal stud 17 and re-entrant cathode envelope segment 12; Independence of the heating potentials and currents is maintained by the provision of a vitreous heater insulator 18, forming a portion of the cathode sleeve 10, and via the dielectric spacing members 16.

Cooling of the external portion of the cathode sleeve 10 is obtained by provision of cooling air which is blown into the re-entrant portion of the cathode assembly through the openings in the perforated header 14, thence through bafile 15, and returned through the annulus formed between bafiie 15-and re-entrant envelope segment 12.

The anode envelope 2 includes tubular envelope segment 21 as of, for example, iron vacuum sealed at one end to the body 1 as by brazing and closed at the other end via cap 20.

The magnetrons magnetic circuit serves to provide an axially directed stronguniform region of magnetic field, which region of magnetic field is tubular and encompasses the outer surface of the cylindrical cathode emitter 9. The magnetic circuit includes a portion external to the evacuated envelope of the magnetron, a portion Within the evacuated envelope of the, magnetron, and a transition portion which also defines the side walls of the evacuated envelope. The external portion of the magnetic circuit includes two C-shaped permanent magnets, not shown, which magnets provide the magnetomotive force for the magnetic circuit. The C-shaped permanent magnets have semicylindrical pole faces for mating with the magnetic envelope portions defined by tubular envelope segments 4 and 21 which segments are made of a good magnetic permeable material such as, for example, soft iron.

The internal anode magnetic circuit includes cylindrical anode magnetic pole piece 25 which is disposed coaxially of and internally of the envelope adaptor segment 21.

The internal cathode pole piece structure includes two coaxial segments. The first coaxial segment is cylindrical pole piece 23. Pole piece 23' is axially aligned with anode pole piece 25 and is disposed in mutually opposing spaced apart relation therefrom thereby forming a gap. The gap forms the region of strong uniform magnetic field necessary to produce magnetron interaction in the regions enveloping the cathode emitter 9.

The second internal cathode pole piece segemnt is cylindrical pole adaptor 22. Pole adaptor 22 is made of a good magnetic permeable material as of, for example, soft iron, and is fixedly secured at one end to cathode flange 6 such that it is fixedly carried at the open end of the detachable portion of cathode envelope 3. The other end portion of the cylindrical pole adaptor 22 envelopes the outer periphery of a portion of cylindrical pole piece 23 and is detachably fastened thereto via soft metal pins 24 driven into aligned openings in pole adaptor 22 and pole piece 23. The pole piece 23 may be readily detached by drilling out the soft metal pins 24 to facilitate assem bly or dismantling of the cathode envelope subassembly. More particularly, once the pins 24 have been removed the cathode envelope subassembly may be readily dismantled by breaking the vacuum joint between the reentrant envelope portion 12 and envelope member 13. The cathode 9 with its dependent sleeve 10 and the attached re-entrant envelope portion 12 is then pulled out of the remaining portion of the cathode envelope 3 from the re-entrant end portion thereof.

Thus, not only is replacement of the cathode assembly facilitated, by splitting of the internal cathode magnetic pole piece structure into the first and second tubular segments 23 and 22, respectively, but also initial fabrication is greatly facilitated in this manner. Initial fabrication is facilitated because the first separate cathode subassernbly may be fabricateod by mating cathode sleeve 10 to the re-entrant envelope segment 12 and making the vacuum tight joint at the junction 11 of sleeve 19 and envelope segment 12. Once the vacuum joint is made at 11 the cathode with pole piece 23 is slidably inserted within the pole adaptor 22 portion of the detachable cathode envelope portion including members 22, 6, 8, 7 and 13 and the seal made at the junction of segments 12 and 13. The two cathode pole piece segments 22 and 23 are then fixedly attached by pins 24 and the complete detachable portion of the cathode envelope inserted into place and the take-apart joint made at mating flanges 5 and 6.

This split internal cathode pole piece structure formed by pole piece 23 and pole piece adaptor 22 represents a substantial improvement, over the prior art wherein these two coaxial pole piece members were effectively one member, since in fabriationa very difficult internal braze had to be made at junction 11.

A typical magnetron interaction region is defined by the cylindrical space between the outer periphery of the cylindrical cathode emitter 9 and the inner tips of an enveloping circular array of radially inwardly directed anode vanes 26. The length of the cylindrical inteaction region is defined at its ends via cathode end hats 30.

The anode vanes 26 are carried attheir outer peripheries from the inside surface of a cylindrical anode wall 27. The spaces between adjacent vanes within the interior of the cylindrical anode wall 27 define a plurality of inner cavity resonators 28, see FIG. 3. An outer coaxial cavity 29 surrounds the inner system of resonators 28. The outer cavity resonator 22 is dimensioned to operate in the TEd mode and the fields of the coaxial resonator 29 are coupled to the inner system of resonator 28 via a plurality of coupling slots 31 in cylindrical anode wall 27. The coupling slots 31 are axailly directed of the magnetron tube apparatus and communicate with alternates ones of the inner cavity resonators 28 to lock the anode resonators to the 1r mode of operation at a frequency controlled by the coaxial cavity 29.

Anode vanes 26 are made approximately an electrical quarter wavelength long in the range of frequencies of the current flowing along the outside surface of anode wall 27, defining the inner wall of outer coaxial resonator 29, such that the high impedance termination at the free ends or tips of the anode vanes 26, is reflected back to coupling slots 31 as a low impedance, and, accordingly, the current flowing along the outside of wall 27 flows into the resonators 28 and inwardly of one of the adjacent,

vanes 26, while on the opposite adjacent vane on the other side of the slot 31, current flows outwardly of the resonator 28 through slot 31. Because such currents are quite high, a high voltage is produced at the tips of vanes 26.

These high voltages, of one phase, appear only across alternate anode vanes 26 at a given time because only alternate inner cavity resonators 28 are coupled by slots 31 to the outer cavity resonator 29. Voltages at the other alternate anode vanes 26 are provided by mutual inductance, resulting in such voltage being 180 out of phase with adjacent vanes. This, of course, is the proper condition for maintenance of the 11' mode of oscillation within the inner resonant system. Hence, the inner system of resonators 28 is effectively locked to the resonant frequency of the outer resonator 29 and controlled by the outer resonator 29 because of its larger volume.

The circumferential directed currents of the TE mode in cavity 29, flowing on the outside of anode cylinder 27, are not uniformly distributed axially of the cylindrical anode Wall 27. On the contrary, the current is highest midway of the axial length of the anode wall 27 and has points of zero magnitude near the ends of the wall. The magnitude of current is indicated approximately by the dotted line 32.

The anode vanes 26 are given a characteristic axeshape in that the height, h, of the vane is tapered downwardly from the free end to the base thereof. The axeshaped anode vane 26 has special utility in this application since it presents a relatively large mass of metal subject to electron bombardment by beam interception at the vane tip to increase the average power handling capability of the tube. The relatively short height of the vane 26, at the base thereof, decreases the losses of the resonator 28. Decreasing the losses associated with the inner system of resonators 28 also lowers the loss coupled into the coaxial cavity resonator 29 thereby increasing the efiiciency of the magnetron tube. Of course, as the height of the base of the vane is decreased, the thermal conducting properties of the vane 26 are diminished. Thus, a compromise between cavity Q and thermal conductivity is made. In a typical example the base of vane 26 is only 75% of the height of the vane 26 at its free end or tip.

The coupling slots 31 act as self-resonant circuits and the characteristic frequency of each slot is dependent upon its inherent capacity and inductance. The magnetic fields produced in each slot tend to link with those of other slots, particularly those which are adjacent. If the slot modes created between individual slots have the same, or nearly the same configuration, a uniform slot mode pattern may be propagated around the entire circumference of cylindrical anode wall 27. Such uniform slot mode pattern tends to interact with the electron stream which flows in the gap between cathode 9 and anode vanes 26, thereby causing spurious oscillations in the inner resonant system and deleteriously affects the stability of the magnetron tube.

Two features are utilized in the present tube to prevent the undesired interaction between the slot mode pattern and the electron beam. One feature is the grouping of the peripheral array of slots 31 into alternating quadrants of different resonant frequency. More specifically, the slots 31 are grouped into four groups, all the slots of the same group having the same resonant frequency and representing 90 of the periphery of the anode cylinder 27. The next 90 of periphery about the anode cylinder has slots 31 of a different frequency. This latter quadrant then is followed by a third quadrant having the same frequency as the first quadrant. Thus, by changing the self-resonant frequency of the groups of slots the build up of a uniform slot mode around the circumference of the anode wall 27 is prevented. This expedient further prevents undesirable bunching of the electrons from persisting throughout their path around the cathode 9.

A lossy slot mode suppressor element or ring 33 forms the second feature for aiding in suppression of the undesired slot mode. The slot mode suppressing element 33 comprises, for example, a carbon impregnated alumina or carbon impregnated beryllium oxide ceramic cylindrical member contained within an annular recess 34 formed in the space between anode pole piece 25 and cylindrical anode wall 27. The cylindrical anode wall 27 forms a heat sinking member for the suppressor ring 33. The suppressor ring 33 is retained within the recess 34 by two loosely fitted pins radially inwardly extending through the wall of the suppressor ring 33 into the anode pole piece 25 to prevent the mode suppressor ring 33 from falling out of the heat sinking retaining recess 34.

In use, the lossy mode suppression member 33 absorbs substantial amounts of power and requires adequate cooling to prevent it from forming a mismatch to the slots due to becoming substantially conductive at high temperatures. Many insulators such as aluminum oxide become semi-conductors at high temperature.

A unique feature of this slot mode absorber design is that the mode absorbing element or ring 33 is dimensioned with respect to the dimensions of the heat sinking anode wall 27 to provide a cold clearance 40 between the outer periphery of mode absorbing element or ring 33 and the outside wall of the heat sinking recess 34 formed by the inner wall of anode cylinder 27. However, the cold clearance 40 is dimensioned such that as the mode absorbing ring 33 is heated, due to absorption of some of the generated power, the dimensions of the mode absorbing element 33 expand radially outwardly causing the outer surface of ring 33 to come into physical contact with the outermost side wall of the retaining recess 34 or innermost wall of anode cylinder 27. Physical contact between the side wall of the suppressor. ring 33 and the cylindrical anode wall 27 produce cooling of the mode absorbing element 33 by thermal conduction to the relatively cool side wall of the recess 34. In an exemplary embodiment of mode absorbing element or ring 33 the mode absorber ring 33 is dimensioned approximately 0.125 inch thick with an outside diameter of approximately 1.4 inches. The cold clearance 40 between the outer periphery of ring 33 and the inside surface of the cylindrical anode wall 27, forming the heat sinking recess 34, is chosen between 0.0005 inch and 0.001 inch. The body portion 1 of the tube operates at a temperature of approximately C., in use.

The inner resonant system of resonators 28, when considered alone, is a usual unstrapped magnetron system which will tend to oscillate in both the 1r and various degenerate modes. The outer cavity resonator 29 is capable of sustaining a number of different modes of operation. However, it is stated above it is dimensioned to operate in the dominant TE mode. Thus, the outer cavity resonator 29 and the inner resonators 28 can be considered as two distinct resonator systems; however, when the two systems are closely coupled together they can be considered to be a single composite system. The outer cavity resonator 2? is capable of oscillating in modes other than the desired TE mode. One of these undesired modes which it is desired to suppress is the TELZJ mode.

A TE mode suppressor is formed by a cylindrical groove choke 35 disposed in one end wall of the outer coaxial cavity 29 and disposed immediately adjacent and outside the cylindrical anode wall 27. The groove choke 35 includes an annular lossy mode suppression member or ring 36 as of, for example, carbonized alumina ceramic disposed in the bottom of the choke 35 and matched to the cavity resonator 29 via an impedance transforming portion 37 of the groove choke 35. The TE mode suppressing choke 35 serves to damp out interfering TE modes having currents tending to flow radially of the coaxial cavity 29, such as the interfering TE mode.

One unique feature of the outer coaxial cavity 29 (see FIG. 4) is the provision of a groove 38 disposed in the fixed end Wall of coaxial cavity 29 and being axially coextensive with both the ends of slots 31 and slot mode absorber 33. The groove 38 is disposed at the intersection of the outer periphery of the cylindrical anode wall 27 with the fixed end wall of coaxial cavity 29. In a preferred embodiment the groove 38 is dimensioned ap proximately 0.143 inch deep and 0.04 inch wide. The depth of the groove 38 is made axially coextensive with the end portions of the coupling slots 31 to prevent shorting of these slots by the fixed end wall.

The minimum width of slot 38 is relatively critical. More specifically, if the minimum Width of groove 38 is only a small fraction of the width w (see FIG. 3) of the adjacently disposed coupling slot 31 portions, which are, for example, 0.033 inch wide, the fixed end wall of the cavity 29 will tend to short out the ends of the coupling slots 31 by adding capacitive coupling across the slots 31 and prevent the mode absorber 33 from being fully effective. If to improve the effectiveness of the slot mode absorber 33 in such a case, it were dimensioned longer such as to cover a greater extent of the slots 31 and thus extend axially a substantial distance past the face of the fixed end wall of cavity 29 it would also couple to the desired TE mode of the coaxial cavity 29 and lower the Q of the desired mode. Thus the portion of the slot mode absorber 33, disposed adjacent the ends of coupling slots 31 is preferably made to be approximately coextensive with the depth of the groove 33 which uncovers the ends of slots 31.

If the maximum width of groove 38 were increased to 0.080 inch wide, the effectiveness of the slot mode absorber 33 would remain unchanged while the Q of the undesired TE mode within the outer cavity 29 would be increased, over that obtained with the optimum width of 0.040 inch, by at least a factor of two. Thus, the groove 38 preferably has a width which lies within the range of one-half to three times the width w of the adjacent coupling slots 31.

Output microwave energy is extracted from the magnetron oscillator via output coupling slot 41, see FIGS. 2 and 3. Output coupling slot 41 is axially directed of the tube and is provided in the outermost wall of coaxial cavity 29. The microwave energy extracted from the resonator 29 is then propagated through an H-shaped impedance transforming section 42 and thence through a section of X-band waveguide 43, and gas tight wave permeable window 44 to a load (not shown).

Cooling of the tube is obtained by two longitudinally spaced interconnected annular coolant chambers 45 provided in the main body portion 1 of the tube. The annular chambers 45 are interconnected via a coolant channet 61 (see FIG. provided in the body portion 1. A plurality of outwardly extending radially directed fins 46 are carried at their base 47 from the innermost wall of the annular chambers 45 and serve to increase thermal conduction from the main body portion 1 to the coolant liquid passing through the annular chambers 45. In use, the coolant fins 46, in communication with the coolant liquid, serve to maintain the main body portion 1 of the magnetron tube at 80 C. when operating at its rated average output power of 1000 watts.

The tube is exhausted during fabrication by the provision of an exhaust tubulation 48 communicating through a central opening in cap 20 with the interior bore of the cylindrical anode pole piece 25. After the tube has been evacuated it is sealed by pinching off the exhaust tubulation at 49.

Since many changes could be made in the above con struction and many apparently widely different embodiments of this invention could be made Without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A coaxial magnetron tube apparatus including, a supporting main body, a cathode envelope structure depending from said main body and capable of being evacuated and detachable from said main body, a cylindrical anode wall member contained within said body, a plurality of vanes extending inwardly from said wall member and defining inner cavity resonators, a cathode positioned within said vanes, means including said wall member defining an outer cavity resonator, said outer cavity resonator having first and second fixed end walls, means for coupling a mode of oscillation of said outer cavity resonator of the 1r mode of oscillation of said inner cavity resonators, said coupling means including slots extending through said wall member for coupling alternate ones of said inner cavity resonators to said outer cavity resonator, an energy absorbing element positioned at the ends of said slots for absorbing the energy stored in said slots, means forming a fluid coolant chamber in said supporting body for cooling said supporting body, in use, magnetic anode and cathode pole piece structures mounted inside said supporting body and positioned on opposite sides of said inner cavity resonators, said cathode magnetic pole piece structure including first and second coaxially disposed tubular magnetic members, said first tubular cathode magnetic member being pinned to said second tubular cathode magnetic member encompassing said first cathode pole member, and said pinned magnetic member being carried from said detachable cathode envelope via the intermediary of said second tubular cathode pole member to facilitate initial construction and the replacement of said cathode, a plurality of said anode vanes having a height at their free ends which is substantially greater than their height at the base of said vanes Where they connect to said anode wall member for decreasing the loss associated with said vanes, said slot energy absorbing element being retained within an annular groove within said body portion and being dimensioned with respect to the dimensions of said retaining groove such that as said energy absorbing element absorbs energy of the unwanted slot mode from within said slot said element will expand and make contact with a side Wall of said retaining groove for enhancing thermal conduction from said absorbing element to said body portion of the magnetron, a second energy absorbing element communicating with the fields of said outer cavity, an annular choke disposed in said first fixed end Wall of said outer cavity resonator and housing said second energy absorbing element, a groove disposed in said second fixed end wall of said outer cavity resonator mutually opposing said cavity end Wall having said second mode absorbing element coupled thereto, said groove serving to increase the exposure of'said slot energy absorbing element to said coupling slots, and means forming a plurality of heat conducting fins disposed within said coolant chamher, said heat conducting fins being connected at their bases to the sidewalls of said coolant chamber and projecting inwardly thereof to enhance thermal conduction from said supporting body portion to a coolant fluid circulating through said coolant chamber in use.

2. A magnetron tube including, an evacuable envelope, a plurality of cavity resonators, magnetic pole pieces mounted inside said envelope and positioned on opposite sides of said resonators, said magnetic pole pieces including a cathode pole piece structure, said cathode pole piece structure including concentrically disposed first and second tubular magnetic members disposed within said evacuable envelope, said second member encompassing said first member, and removable fasteners interconnecting said first and second tubular members within said evacuable envelope to facilitate fabrication and disassembly of the magnetron apparatus.

3. The apparatus according to claim 2 wherein, said cathode pole piece structure includes a third tubular magnetic member coaxially disposed externally of. said first and second cathode pole magnetic members and disposed in enveloping abutting relationship with said second member, said third magnetic member forming a portion of said evacuableenvelope of the magnetron tube, means for generating a magnetomotive force and said generating means mating with said third magnetic member and disposed outside of said evacuable envelope portion of the magnetron tube.

4. In an electronic oscillator circuit, means defining a first cavity resonator, means defining a second system of resonators, a common wall member separating said first cavity resonator from said second system of resonators, said second system of resonators including a plurality of vanes connected at their bases to and extending from said common wall, said common wall having a plurality of elongated coupling slots therein for wave communication between said first cavity resonator arid said second system of resonators, said coupling slots serving to excite said vanes with current derived from currents flowing within said first cavity resonator, and said vane members having a height at their base taken in the direction of elongation of said coupling slots which is substantially less than the height at their free end portions to reduce losses associated with currents flowing in said second system of resonators.

5. The apparatus according to claim 4 including wave energy dissipating means disposed adjacent said coupling slots for selectively damping unwanted oscillations which cause energy storage in said slots.

6. The apparatus according to claim 4, wherein said first cavity resonator means is dimensioned to support a dominant circular electric mode of oscillation.

7. The apparatus according to claim 4, wherein said vane members have a height at their base which tapers uniformly to a greater height at their free end portions to enhance thermal conduction of said tapered vanes.

8. In a coaxial magnetron oscillator apparatus, a cylindrical wall member, a plurality of vanes extending inwardly from said wall member and defining inner cavity resonators, a cathode positioned within said vanes, means including said wall member defining an outer cavity resonator encompassing said inner cavity resonators, means for coupling alternate ones of said inner cavity resonators to said outer cavity resonator, said coupling means including axially directed slots extending through said wall member beyond the ends of said vanes, said vanes having free end portions remote from said cylindrical wall member and base portions where said vanes connect to said wall member, and the axial height of said vanes being substantially greater at their free end portions than at their base portions to increase the Q of said inner cavity resonators.

9. In a magnetron oscillator apparatus, a cylindrical cathode for forming and projecting a stream of electrons, a cylindrical anode wall surrounding said cathode and disposed coaxial therewith, an array of anode vanes extending radially inwardly from said anode wall and defining a plurality of anode resonators, means including said anode wall defining an outer cavity resonator, means for coupling certain ones of said anode resonators with said outer resonator, said coupling means including a plurality of adjacent slots extending through said cylindrical anode wall into a plurality of said anode resonators, said slots having an axial length substantially greater than the axial extent of said anode vanes, said anode vanes having free end portions remote from said cylindrical anode wall and base portions at the intersection of said anode vanes with said anode wall, and the axial height of said anode vanes being substantially greater at the free end portions thereof than at the base portions thereof to increase the Q of said anode resonators.

10. In a cross field tube apparatus, a cathode, an anode wall with a plurality of vanes extending therefrom and defining a plurality of anode resonators adjacent to said cathode, means for defining with said anode wall a sec- 0nd cavity resonator, means for coupling alternate ones of said anode resonators to said second cavity resonator and including a plurality of slots communicating through said anode wall between said anode resonators and said second cavity resonator, dissipative means positioned at the ends of said slots for selectively damping unwanted oscillations which cause energy storage in said slots, said dissipative means including a lossy element, a heat sinking member, said lossy element being disposed adjacent and spaced slightly from said heat sinking member, said lossy element being dimensioned with respect to the space between said heat sinking member and said lossy member such that as said lossy member is heated due to absorption of generated R.F. energy therein said lossy member will expand and make contact with said heat sinking member to produce thermal cooling to said lossy member in use.

11. A cross field tube apparatus according to claim 10 including, a supporting main body portion, and said body portion having an annular fluid coolant chamber therein, said fluid chamber having a plurality of heat conducting fins projecting inwardly of said chamber from the side walls thereof, and means for passing a fluid coolant through said chamber for removing thermal energy generated Within said main body portion by conduction to said fluid coolant via said heat conducting fins whereby overheating of said main body portion is prevented in use.

12. A tube apparatus according to claim 10 including, metallic supporting body portion enveloping said anode resonators and said outer cavity resonators, said metallic supporting body having axially spaced apart annular liquid coolant chambers at opposite ends of said outer cavity resonator, said annular liquid coolant chambers being interconnected via a coolant passage in said metallic supporting body, and said annular coolant chambers having a plurality of annular cooling fins inwardly projecting of said annular coolant chambers from the innermost wall thereof for enhancing thermal conduction of energy from said metallic supporting body to said liquid coolant passing through said coolant chambers.

13. In a magnetron apparatus, a cylindrical wall memher, a plurality of vanes extending inwardly from said Wall member and defining inner cavity resonators, a cathode positioned within said vanes, means including said wall member defining an outer cavity resonator encompassing said inner cavity resonators, means for coupling alternate ones of said inner cavity resonators to said outer cavity resonator, said coupling means including axial slots extending through said wall member beyond the ends of said vanes, and means positioned at the ends of said slots for selectively damping unwanted oscillations which cause energy storage in said slots, said damping means including a lossy member disposed inwardly of said wall member and adjacent thereto, said lossy element dimensioned to provide a cold clearance between said loosy member and said cylindrical wall member, and said lossy member dimensioned such that energy absorbed by said lossy element produces thermal expansion of said element, in use, to cause said lossy element to expand radially outwardly against said wall member to produce thermal conduction from said lossy element to said wall member for cooling of said lossy element.

14. In a magnetron apparatus, a body portion, an outer cavity resonators sustaining a TE mode of oscillation and having a cylindrical inner wall, a plurality of cavity resonators within said inner wall, means for locking the 1r mode of oscillation of said plurality of cavity resonators to said TE mode of said outer cavity resonator, said means including axial slots extending through said inner wall member at alternate ones of said inner cavity resonators, and vanes defining said inner cavity resonators, each of said vanes being approximately an electrical quarter wavelength long at the frequency of said outer cavity resonator, and a ring of lossy material disposed adjacent the ends of said slots for loading of unwanted modes of oscillation of said inner cavity resonators only, said unwanted modes being characterized by storage of energy in said slots, said ring of lossy material being disposed within an annular groove in the said body portion of the tube, said ring of lossy material loosely fitting within said groove by having a thickness slightly less than the width of said groove when cold, and the cold clearance between said lossy ring and the outer ring encompasing side wall of said groove being dimensioned such that as the lossy ring is heated by absorption of energy, in use, the ring expands radially outwardly to make physical contact with the outer ring encompassing side wall of said groove to produce thermal conduction from said lossy ring to the body portion of the tube.

15. The apparatus according to claim 14 wherein said lossy ring is made of carbon impregnated alumina ceramic.

16. The apparatus according to claim 14 wherein said lossy ring is made of carbon impregnated beryllium oxide ceramic.

17. In a magnetron oscillator apparatus, a body portion, a circular electric mode cavity resonator sustaining a TE mode of oscillation and having a cylindrical boundary wall, a system of resonators projecting from said cylindrical wall on the side thereof remote from said TE cavity resonator, means for locking the 1r mode of oscillation of said system of resonators to the TE mode of said cavity resonator, saidlocking means including axial slots extending through said cylindrical wall member at alternate ones of said resonators of said system of resonators, a plurality of vanes defining said system of resonators, each of said vanes being approximately an electrical quarter wave length long at the frequency of said TE mode resonator, a ring of lossy material disposed adjacent to the ends of said slots for loading of unwanted modes of oscillation of vsaid'system of resonators only, said unwanted modes being characterized by storage of energy in said slots, said vanes having free end portions remote from said cylindrical Wall and base portions where said vanes connect to said cylindrical wall member, and the axial height of said vanes tapering in height from their base portions to a substantially increased height at their free end portions to increase the Q of said system of resonators and said circular electric mode resonator.

References Cited by the Examiner UNITED STATES PATENTS 2,482,495 9/49 Laidig 315-3975 2,815,469 12/57 Sixsmith 31530.77 2,821,659 1/58 Feinstein 31539.77 2,854,603 9/58 Collier et al. 315-3977 3,032,680 5/62 Olson 31539.77 X

FOREIGN PATENTS 641,020 5/62 Canada.

ARTHUR GAUSS, Primary Examiner.

GEORGE N. WESTBY, Examiner. 

14. IN A MAGNETRON APPARATUS, A BODY PORTION, AN OUTER CAVITY RESONATORS SUSTAINING A TE-0,1, 1 MODE OF OSCILLATION AND HAVING A CYLINDRICAL INNER WALL, A PLURALITY OF CAVITY RESONATORS WITHIN SAID INNER WALL, NEANS FOR LOCKING THE N MODE OF OSCILLATION OF SAID PLURALITY OF CAVITY RESONATORS TO SAID TE0,1,1 MODE OF SAID OUTER CAVITY RESONATOR, SAID MEANS INCLUDING AXIAL SLOTS EXTENDING THROUGH SAID INNER WALL MEMBER AT ALTERNATE ONES OF SAID INNER CAVITY RESONATORS, AND VANES DEFINING SAID INNER CAVITY RESONATORS, EACH OF SAID VANES BEING APPROXIMATELY AN ELECTRICAL QUARTER WAVELENGTH LONG AT THE FREQUENCY OF SAID OUTER CAVITY RESONATOR, AND A RING OF LOSSY MATERIAL DISPOSED ADJACENT THE ENDS OF SAID SLOTS FOR LOADING OF UNWANTED MODES OF OSCILLATION OF SAID INNER CAVITY RESONATORS ONLY, SAID UNWANTED MODES BEING CHARACTERIZED BY STORAGE OF ENERGY IN SAID SLOTS, SAID RING OF LOSSY MATERIAL BEING DISPOSED WITHN AN ANNULAR GROOVE IN THE SAID BODY PORTION OF THE TUBE, SAID RING OF LOSSY MATERIAL LOOSELY FITTING WITHIN SAID 